This invention relates to apparatus for controlling the alignment of moving webs and has particular application to collators. Typical collators for such application of the invention are shown in Schriber U.S. Pat. No. 3,682,468. In such collators a plurality of marginally perforated webs of paper are directed horizontally toward a series of spaced rollers and thence downwardly toward a horizontally moving pin conveyor. Just prior to reaching the conveyor the webs engage feed wheels which guide them into accurately registered overlying relationship against the conveyor. For satisfactory operation of the collator it is necessary to control the alignment of the moving webs to a high degree of accuracy. There has been an ever increasing need to control the accuracy of such web placement and to ease the job of the operator responsible therefor.